Method for producing hydrogenated polygermane and hydrogenated polygermane

ABSTRACT

A process for preparing hydrogenated polygermane as a pure compound or mixture of compounds, including hydrogenating halogenated polygermane.

RELATED APPLICATIONS

This is a §371 of International Application No. PCT/EP2010/068979, with an international filing date of Dec. 6, 2010 (WO 2011/067411, published Jun. 9, 2011), which is based on German Patent Application No. 10 2009 056 731.3 filed Dec. 4, 2009, the subject matter of which is incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to a process for preparing hydrogenated polygermane, and also hydrogenated polygermane as a pure compound or mixture of compounds.

BACKGROUND

Known processes for preparing polygermane are carried out with GeH₄ as starting material, with, the consequences first that it is necessary to deal with substances which are hazardous to health and that the yields obtained are often low. In particular, it has to date not been possible to prepare longer-chain compounds in a targeted way.

Polygermanes are known from U.S. 2007/0078252 A1, for example.

It could be helpful to provide a process for preparing hydrogenated polygermane that exhibits an improved yield relative to known processes and avoids GeH₄ as a starting material, and also to provide hydrogenated polygermane having improved properties.

SUMMARY

We provide a process for preparing hydrogenated polygermane as a pure compound or mixture of compounds including hydrogenating halogenated polygermane.

We also provide a hydrogenated polygermane as a pure compound or mixture of compounds including substituents Z which comprise hydrogen, a ratio of Z to germanium of at least 1:1, an averaged formula GeZ_(x), where x is 1≦x≦3, and an average chain length n with 2≦n≦100.

We further provide a germanium layer produced from a hydrogenated polygermane.

We still further provide a method for producing a germanium layer on a substrate, including applying a solid or dissolved hydrogenated polygermane to a substrate; and pyrolyzing the hydrogenated polygermane.

DETAILED DESCRIPTION

We provide a process for preparing hydrogenated polygermane as a pure compound or mixture of compounds, where halogenated polygermane is hydrogenated. Hydrogenated polygermane may mean, for example, a pure compound or a mixture of compounds which in each case have at least one direct bond between two germanium atoms. The hydrogenated polygermane may have substituents Z comprising hydrogen, a ratio of Z to germanium GeZ_(x) of at least 1:1, an averaged formula x, where x is selected from 1≦x≦3, preferably 1.5≦x≦3, more preferably 2≦x≦3, and an average chain length n with 2≦n≦100.

The term “pure compound” is understood below to mean that the hydrogenated polygermane comprises compounds having no differences in their chain length, if present in their branches and/or in the number and nature of their rings. In other words, only one fraction of hydrogenated polygermane is present in a pure compound. “Pure” here is to be understood in accordance with typical fine-chemicals yardsticks. Accordingly, even pure compounds may include small fractions of impurities, examples being traces of carbon or halogens, or small fractions of different hydrogenated polygermanes. Small fractions in this context are less than 0.5 mol %, preferably less than 10 ppm.

Analogously, “mixture of compounds” is understood below to mean that the hydrogenated polygermane has at least two fractions whose hydrogenated polygermanes differ in their chain length, if present in their branches and/or in their nature and number of rings.

Accordingly, either all of the molecules of the pure compound or all of the molecules of the at least two fractions of the mixture of compounds may in each case have at least one direct bond between two germanium atoms.

We thus provide a process for preparing hydrogenated polygermane with which for longer-chain polygermanes in particular, the yields are increased relative to known preparation processes. By virtue of the fact that hydrogenated polygermane is prepared from halogenated polygermane, the structure present in the halogenated polygermane may also be largely retained in the hydrogenated polygermane or may be coincident with that structure.

“Largely” in this case means at least 50%. During hydrogenation, however, there may also be rearrangements of the existing structure of the halogenated polygermane resulting, for example, in more branches in the hydrogenated polygermane than were present in the starting material, the halogenated polygermane. However, according to the halogenated polygermane from which they are prepared, the hydrogenated polygermanes prepared by the process may remain distinguishable.

With the process it is possible to prepare pure compounds or mixtures of compounds of fully hydrogenated polygermanes which have the general formula Ge_(x)Hy with x≧2, x≦y≦2x+2. Preparation takes place by hydrogenation of halogenated polygermanes of the general formula Ge_(x)X_(y) with x≧2, X=F, Cl, Br, I, x≦y≦2x+2.

It is possible with this process to prepare hydrogenated polygermanes and also hydrogenated oligogermanes. Hydrogenated oligogermanes have a chain length n selected from the range 2≦n≦8. Their empirical formula is Ge_(n)Z_(2n+2) or the average empirical formula of the mixture Ge_(n)Z_(2n), where Z is the substituent and comprises hydrogen. Hydrogenated polygermanes have chain lengths n of n>8 and an empirical formula Ge_(n)Z_(2n+2) or the average empirical formula of the mixture Ge_(n)Z_(2n). In principle, chain lengths of 2≦n≦6 are referred to as short-chain, and chain lengths of n>6 as long-chain. By “chain length” is meant the number of germanium atoms joined to one another directly.

The halogenated polygermane may be selected from thermally prepared halogenated polygermane and plasma-chemically prepared halogenated polygermane. Thermally prepared halogenated polygermane may have a higher fraction of branches than plasma-chemically prepared halogenated polygermane, which may be largely free from branches. The halogenated polygermanes may be pure compounds or mixtures of compounds.

A process for preparing plasma-chemically prepared halogenated polygermane is disclosed in U.S. 2010/0155219, the subject matter of which is incorporated herein by reference.

The halogenated, more particularly highly halogenated, polygermanes may have substituents selected from the group encompassing F, Cl, Br, and I, and mixtures thereof. During hydrogenation, these halogens may be replaced largely completely by H as a substituent. Largely completely here means at least to an extent of 50%. The halogen content of the hydrogenated polygermane prepared by this process may be less than 2 atom %, more particularly less than 1 atom %. A hydrogenated polygermane may therefore have exclusively hydrogen, or hydrogen and a halogen, chlorine, for example, as substituents Z.

The chlorine content of a compound or of a mixture, i.e., both of chlorinated polygermane and of a hydrogenated polygermane prepared therefrom, is determined by complete digestion of the sample and subsequent titration of the chloride by the method of Mohr. The H content is determined by integration of ¹H NMR spectra, using an internal standard, and comparison of the resultant integrals, where the mixing ratio is known. The molar masses of the halogenated and hydrogenated polygermanes, and the average molar mass of the halogenated and hydrogenated polygermane mixtures, are determined by freezing-point depression. From the stated variables it is possible to determine the ratio of halogen and/or hydrogen to germanium.

The halogenated polygermane can be reacted with hydridic hydrogenating agents selected from metal hydrides and/or metalloid hydrides. Metal hydrides and/or metalloid hydrides also include mixed metal hydrides and/or metalloid hydrides, respectively, in other words, hydrides which contain different metals and/or metalloids or a metal and an organic radical. The hydrogenating agents may be selected from a group encompassing MH, MBH₄, MBH_(4−x)R_(x), MAlH₄, AlH_(x)R_(3−x), and suitable mixtures thereof. Examples of such agents are LiAlH₄, DibAlH (diisobutyl=Dib), LiH, and HCl. Preference is given to mild hydrogenating agents which permit hydrogenation of halogenated polygermane without alteration of the germane backbone.

Hydrogenation can be carried out at a temperature encompassing −60° C. to 200° C. The temperature range may preferably be −30° C. to 40° C., more particularly −10° C. to 25° C. Furthermore, the hydrogenation may be carried out at a pressure encompassing 1 Pa to 2000 hPa, preferably 1 hPa to 1500 hPa, more preferably 20 hPa to 1200 hPa. Accordingly, gentle hydrogenation conditions are set up, with pressures and temperatures lower in comparison to the prior art. In this way, even the less-stable halogenated polygermanes can be hydrogenated with a good yield and a high conversion rate.

The halogenated polygermane can be diluted in a solvent prior to the hydrogenation. The solvent in this case is selected such that it is inert toward the halogenated polygermane—that is, does not enter into any chemical reaction with it. Inert solvents selected may be alkanes or aromatics, examples being benzene, toluene or hexane. Mixtures of solvents are conceivable as well. The hydrogenation may alternatively be carried out with undissolved halogenated polygermane as well.

With this process, therefore, hydrogenated polygermane can be prepared in a good yield, in any desired chain length, and with precursors that present little hazard. Moreover, by a suitable selection of the precursors, it is possible largely to dictate the structure of the hydrogenated polygermane. Furthermore, a largely complete hydrogenation of the hydrogenated polygermane can be achieved with this process.

Additionally specified is a hydrogenated polygermane as a pure compound or mixture of compounds. The hydrogenated polygermane has substituents Z comprising hydrogen, a ratio of Z to germanium of at least 1:1, an averaged formula GeZ_(x), where x is selected from 1≦x≦3, preferably 1.5≦x≦3, more preferably 2≦x≦3, and an average chain length n with 2≦n≦100. Hydrogenated polygermane may be, for example, a pure compound or a mixture of compounds which in each case have at least one direct bond between two germanium atoms.

With regard to the terms “pure compound” and “mixture of compounds”, the statements already made in connection with the process apply analogously. It is the case in turn that “pure” is understood under typical fine-chemicals yardsticks. Accordingly, even pure compounds may include small fractions of impurities, examples being traces of carbon of halogens. Small fractions here are less than 0.5 mol %, preferably less than 10 ppm.

“Chain length” means the number of germanium atoms attached to one another directly. The chain length of the hydrogenated polygermane may be selected more particularly from 4≦n≦50, more particularly from 6≦n≦20.

The averaged formula GeZ_(x) is to be understood, accordingly, to mean that a germanium atom in the hydrogenated polygermane has on average 1 to 3 substituents Z. Taken into account here are the germanium atoms both in linear polygermanes and also in rings or branched polygermanes. A hydrogenated polygermane of this kind is suitable for a multiplicity of applications on the basis of its chemical properties.

The hydrogenated polygermane may have been prepared by a process according to the statements above. Accordingly it is prepared by hydrogenation of halogenated polygermanes. Through the preparation process, therefore, the structure of the hydrogenated polygermane may be derivable from the structure of the halogenated polygermane or may be coincident with it.

For example, largely linear hydrogenated polygermanes may be obtained by hydrogenating plasma-chemically prepared halogenated polygermanes or hydrogenated polygermanes having a high fraction of branches may be obtained by hydrogenating thermally prepared halogenated polygermanes. Hydrogenation may be carried out largely completely, and so the substituents Z in the polygermane largely comprise hydrogen. “Largely” here means again a fraction of hydrogen among the substituents of at least 50%. Hydrogenation, however, may also proceed to completion, giving a 100% fraction of hydrogen as substituent Z.

The hydrogenated polygermane may have a fraction of polygermane molecules having more than three directly connected germanium atoms with at least 8%, more particularly more than 11%, of the germanium atoms being branching sites. The fraction of polygermane molecules having more than three directly connected germanium atoms in this case may be a pure compound, or may be a fraction of the hydrogenated polygermane in the case of a mixture of compounds. In each case, such polygermane molecules have a chain length of n>3. The term “branching sites” refers to those germanium atoms connected to more than two other germanium atoms, in other words having only one substituent Z or none at all. Branching sites may be determined by ¹H NMR spectra, for example.

The hydrogenated polygermane which is a mixture of compounds may in the form of the mixture have a higher solubility than at least one individual compound which is present in the mixture. Hence, at least one individual component of the mixture has a lower solubility than the individual component in conjunction with the other components of the mixture of compounds. The reason that lies behind this is that the different components of the mixture act mutually as solubilizers. In principle, shorter-chain molecules have a better solubility than their longer counterparts, and so in a mixture of compounds they also improve solubility of the longer-chain molecules.

The hydrogenated polygermane may have a fraction of polygermane molecules having more than three directly connected germanium atoms, with these polygermane molecules having an averaged formula GeZ_(x) with 2.2≦x≦2.5. More particularly, x may be selected from 2.25≦x≦2.4.

Furthermore, the hydrogenated polygermane may have a substituent Z which additionally comprises a halogen. Accordingly, as well as hydrogen, the hydrogenated polygermane may also have halogens, examples being F, Br, I or Cl, or mixtures thereof, as substituents. In this case, the fraction of halogen in the hydrogenated polygermane may be less than 2 atom %, more particularly less than 1 atom %. Provided accordingly is a largely hydrogenated polygermane which has only a low fraction of halogen substituents.

Furthermore, the hydrogenated polygermane may have a fraction of hydrogen which is greater than 50 atom %, preferably greater than 60atom %, more particularly greater than 66 atom %. The hydrogenated polygermane thus has a very high fraction of hydrogen, whereby the ratio of substituent to germanium of at least 1:1 is established in conjunction with a high hydrogen content.

In ¹H NMR spectra, the hydrogenated polygermane may have significant product signals in the chemical shift range of 6.5 to 2.0, more particularly 4.0 to 2.1 ppm. “Significant” in this context means that an integral is greater than 1% of the total integral. Furthermore, in ¹H NMR spectra, the hydrogenated polygermane may have at least 80% of the signal intensity of the total integral of its significant product signals in the chemical shift range of 3.6 to 2.9 ppm.

Furthermore, in Raman spectra, the hydrogenated polygermane may have significant product bands in the range from 2250 to 2000 wavenumbers and at below 330 wavenumbers. “Significant” in connection with Raman spectra means more than 10% of the intensity of the highest peak.

The hydrogenated polygermane may be colorless to pale yellow or ivory. It may be present as an amorphous or crystalline solid. It is preferably not of high viscosity.

Furthermore, the hydrogenated polygermane may be soluble to an extent of at least 20% at concentrations of up to 10% in inert solvents. This means that at least one compound of a mixture of compounds of the hydrogenated polygermane is readily soluble in inert solvents. Inert solvents are those solvents which do not react with the hydrogenated polygermane. It is possible, for example, to select solvents selected from a group encompassing benzene, toluene, cyclohexane, SiCl₄, and GeCl₄.

The readily soluble hydrogenated polygermane of the aforementioned mixture of compounds may be distillable and/or volatile without decomposition under reduced pressure to an extent of more than 20%, preferably to an extent of more than 80%. The reduced pressure in this case comprises preferably 1 to 100 Pa. Accordingly, the hydrogenated polygermane can be isolated effectively.

We additionally provide a germanium layer produced from a hydrogenated polygermane according to the description above.

The hydrogenated polygermane is a starting compound readily available on the industrial scale for production of germanium layers. As a result of the low pyrolysis temperature of less than 500° C., preferably less than 450° C., the hydrogenated polygermane is a precursor with which it is possible, at a low temperature, to deposit germanium layers on substrates. The low pyrolysis temperature permits a relatively large selection of materials for the carrier layers and substrates to which germanium layers are applied, examples being carrier layers of glass. Moreover, diffusion of impurities from the carrier material into the resultant germanium layer will be diminished or avoided.

A method for producing a germanium layer on a substrate comprises the method steps of A) applying a solid or dissolved hydrogenated polygermane according to the statements above to a substrate and B) pyrolyzing the hydrogenated polygermane. This method leads, with high yields and high conversion rates, to germanium layers produced from hydrogenated polygermanes. The hydrogenated polygermanes can be processed with a higher yield and a higher conversion rate than conventional germanium precursors to form germanium layers. In this context, dissolved or else solid hydrogenated polygermanes can be applied in an easy way to the substrate. CVD (chemical gas-phase deposition), PVD (physical gas-phase deposition) of plasma deposition is therefore not necessary. Provided, therefore, is a simplified method for producing germanium layers.

For the hydrogenated polygermanes, additionally possible are applications in germanium chemistry as, for example, production of conductive polymers, light-emitting diodes or other components.

Indicated below is a working example that relates to preparation of a hydrogenated polygermane.

A polychlorogermane (PCG) generated by plasma reaction of GeCl₄ with H₂ takes the form of a viscous oil or a solid, each with a color of yellow to orange-brown. 8.5 g (60 mmol GeCl₂ equivalents) of the PCG are admixed with 40 ml of absolute benzene and undergo partial dissolution as a result. At 0° C., 26 ml of diisobutylaluminum hydride (145 mmol, about 20% excess) are added dropwise over the course of 30 minutes. Over the course of about 1 hour, the orange sediment is consumed by reaction to form a pale yellow powder. The reaction mixture is subsequently stirred for 16 hours, during which it is warmed at room temperature. The solid is isolated by filtration and washed with twice 25 ml of absolute hexane. After drying under reduced pressure, 2.1 g of hydrogenated polygermane are isolated.

Our compositions and methods are not restricted by this disclosure on the basis of the working examples. Instead, the disclosure encompasses every new feature and also every combination of features which includes, in particular, any combination of features in the appended claims, even if that feature combination is itself not explicitly specified in the claims or working examples. 

1.-24. (canceled)
 25. A process for preparing hydrogenated polygermane as a pure compound or mixture of compounds comprising hydrogenating halogenated polygermane.
 26. The process according to claim 25, where the halogenated polygermane is selected from the group consisting of thermally prepared halogenated polygermane and plasma-chemically prepared halogenated polygermane.
 27. The process according to claim 25, where the halogenated polygermane is reacted with at least one hydridic hydrogenating agent selected from the group consisting of metal hydrides and metalloid hydrides.
 28. The process according to claim 27, where the hydrogenating agent is at least one selected from the group consisting of a MH, MBH₄, MBH_(4−x)R_(x), MAlH₄ and AlH_(x)R_(3−x).
 29. The process according to claim 25, where hydrogenation is carried out at a temperature of −60° C. to 200° C.
 30. The process according to claim 25, where the hydrogenation is carried out at a pressure of 1 Pa to 2000 hPa.
 31. The process according to claim 25, where the halogenated polygermane is diluted in a solvent prior to hydrogenation.
 32. A hydrogenated polygermane as a pure compound or mixture of compounds comprising: substituents Z which comprise hydrogen; a ratio of Z to germanium of at least 1:1, an averaged formula GeZ_(x), where x is 1≦x≦3, and an average chain length n with 2≦n≦100.
 33. The hydrogenated polygermane according to claim 32, prepared by a process comprising hydrogenating halogenated polygermane.
 34. The hydrogenated polygermane according to claim 32, having a fraction of polygermane molecules having more than three directly connected germanium atoms, where at least 8% of these germanium atoms are branching sites.
 35. The hydrogenated polygermane according to claim 32, which is a mixture of compounds having a higher solubility than at least one individual compound present in the mixture.
 36. The hydrogenated polygermane according to claim 32, having a fraction of polygermane molecules having more than three directly connected germanium atoms, where the polygermane molecules have an averaged formula GeZ_(x) where 2.2≦x≦2.5.
 37. The hydrogenated polygermane according to claim 32, where Z additionally comprises halogen. 38 The hydrogenated polygermane according to claim 37, where a fraction of halogen is less than 2 atom %.
 39. The hydrogenated polygermane according to claim 32, where a fraction of hydrogen is greater than 50 atom %.
 40. The hydrogenated polygermane according to claim 32, which in ¹H NMR spectra has significant product signals in a chemical shift range of 6.5 to 2.0 ppm.
 41. The hydrogenated polygermane according to claim 32, which in ¹H NMR spectra has at least 80% of a signal intensity of a total integral of its significant product signals in a chemical shift range of 3.6 to 2.9 ppm.
 42. The hydrogenated polygermane according to claim 32, which in Raman spectra has significant product bands of 2250 to 2000 wavenumbers and at below 330 wavenumbers.
 43. The hydrogenated polygermane according to claim 32, which is colorless to pale yellow or ivory.
 44. The hydrogenated polygermane according to claim 32, which is amorphous or a crystalline solid.
 45. The hydrogenated polygermane according to claim 32, which is soluble at least to an extent of 20% at concentrations of up to 10% in inert solvents.
 46. The hydrogenated polygermane according to claim 45, where the soluble hydrogenated polygermane is distillable and/or volatile without decomposition to an extent of more than 20% under reduced pressure.
 47. A germanium layer produced from a hydrogenated polygermane according to claim
 32. 48. A method for producing a germanium layer on a substrate, comprising: applying a solid or dissolved hydrogenated polygermane according to claim 32 to a substrate; and pyrolyzing the hydrogenated polygermane. 